1. Field of the Invention
The present invention relates to a sheet conveying apparatus provided with a spherical conveying rotation member and a driven rotation member pressed with the conveying rotation member so that a sheet is nipped to be conveyed by these members, and an image forming apparatus provided with such a sheet conveying apparatus.
2. Description of the Related Art
In general, image forming apparatuses, such as those of an electrophotographic system, an offset printing system, and an inkjet system, have been known. In recent years, in these image forming apparatuses, there have been increasing demands for a technique, upon conveying a sheet, the posture of the sheet is corrected with high precision. Normally, by correcting a skew feeding of a sheet and a positional deviation in the width direction thereof, the posture of the sheet is corrected so that positions of the sheet and an image to be formed are adjusted. Moreover, a technique by which the posture of a sheet is corrected so that a conveying defect, such as a jam, is avoided, and a technique by which the sheet posture is corrected so that the sheet edge is avoided from being made in contact with a roller that is a consumable product at the same position, thereby prolonging the service life of the consumable products against damages, have been proposed. In another technique, the posture of a sheet is corrected so as to convey the sheet to a post processing device for a book-binding process.
Moreover, a structure has been proposed in which a reference guide and a spherical conveying ball that carries out a pulling-over action to the reference guide are installed so as to correct a positional deviation in the width direction of a sheet such as copy paper (see Japanese Patent Application Laid-Open No. 2002-308474). In Japanese Patent Application Laid-Open No. 2002-308474, two rotation rolls are disposed on the upstream side of the conveying ball and at a position with an angle of 90° relative to the width direction so as to be pressed with the equator of the conveying ball so that by changing the pressing force of the rotation rolls to the conveying ball, the rotation direction of the conveying ball is altered. The rotation rolls are driven to rotate by a rotation driving motor, and in order to change the pressing force of the rotation rolls, a pressing force variable motor is installed in a separate manner.
However, in the above-mentioned conventional structure, since the conveying ball is pressed by the rotation rolls to change the rotating direction, the equator portion of the conveying ball needs to be supported by a ball supporting member so as not to move the conveying ball by the pressing force of the rotation rolls. Since the conveying ball is pressed onto the ball supporting member by the pressing force of the rotation rolls, a frictional force is changed between the conveying ball and the ball supporting member depending on the pressing force of the rotation rolls. In the case when the frictional force between the conveying ball and the ball supporting member is changed in this manner, the rotation of the conveying ball becomes unstable. Moreover, when the pressing force of the rotation rolls is large, the frictional force between the conveying ball and the ball supporting member becomes excessively large to sometimes cause a difficulty in smoothly altering the rotation direction of the conveying ball.
Therefore, the objective of the present invention is to provide a sheet conveying apparatus and an image forming apparatus that can carry out a stable frictional driving operation on the conveying rotation member with a simple structure so that the posture of the sheet can be easily corrected.